With engine OFF, Move the tach needle counterclockwise until it's at 0 RPMS. Start the engine. The RPMS should be around 800 or so. You might have to pull out clock needles in order to move the tach needle counterclockwise.
a 12v line is to the clock. then there is a Power +12v line as a power source to the tach then there is a signal wire that goes to the pickup that's in front/above of the engine crankshaft pulley then the body of the unit is the 'ground' so make sure it's nice and screwed into the back of the instrument cluster.
